COMP Cams® recommends ensure the proper pre-load.
" Hydraulic lifters have the ability to automatically adjust themselves and maintain zero clearance in the valve train by supporting the pushrod plunger on a small chamber of pressurized oil, regulated by a precisely controlled oil bleed rate. Valve train noise is prevented because the lifter is preloaded, eliminating any clearance.
Hydraulic lifter preload is the distance the pushrod plunger is depressed below the retaining lock. Preload should be between .020"-.060" for the lifter to perform properly. With too little preload, the valve train will be noisy and the retaining lock may fail (break or pop out) due to excessive hydraulic force against the retainer. Conversely, too great a preload (more than .060") will produce excessive lifter pump-up, causing the valves to open longer and lift higher, drastically reducing cylinder pressure and hurting engine performance. The engine will also have very low vacuum, causing it to idle very poorly. "

The Base circle on the r53 camshaft is 1.185 inch. when you remove the material off the Base circle ( to increase the valve lift , or add duration) you will make the base circle smaller. ( ie: 1.185 stock to a 1.120 modified), this will allow the lifter to extend and remove the correct amount of Pre-load.
By adding a 'Lash Cap' to the top of the valve tip, you can remove the distance loss of .045" in base circle, ( this example) and bring the lifter back to the correct position ( Factory set Per-load ).
The example here is the Schrick Cam. On the Exhaust lobe it contacts the spark plug tube, and we are advised to "ding " the tube for clearance. With the stock BMW base circle and the total lobe lift.. the Cam has a 8.9 mm lift at the Valve ( .352" !!) Therefor ANY camshaft for the r53, that has more lift at the Exhaust Valve of 8.9 mm ... HAS TO HAVE a smaller base circle and thus removing the 'factory pre-load'.

Is this a critical area for performance ?? LOL, YEP !!

Hope this helps when you are building or just changing camshaft.
Thumper Performance

Racing is a demanding sport !! Power and torque curves are all important !! Bearing longivity at high RPM is critle, Choosing a camshaft for your Track and Performance level. Indexing the Camshaft for the power when you need it. Getting powerful boosted the air in and then out is a major factor. Valvetrain operation.. valve guide wear, or those racing springs wear when busting 7800-8000 revs !! OMG.. this sport is demanding.. as they say, IT is only a Hobby !! WTF !! hobby?? sure! Bounce that statement off your Wife a few times !! LOL

We have a 'install and forget it' rocker arm assy's.. right?? Throw in a camshaft and rock !! Oh Hell yeah !!

But with the Hydrolic lifters we use ( designed to not need adjustment).. there is a certain 'Pre-load ' that is required to keep and maintaing the correct pressure on the lifter to allow the valve to open at the designed 'Lift' on the camshaft.. or even stay open for the duration it was intended for. Cam manufactures know this.. engine builders know this. IF you remove some 'pre-load off the lifter.'. the valve will not open as far as it is intended. Example a .400 Lift cam will only be in there at .385 " Lift. Shit !! just wasted all that money on less performance than you expected!!

Well screw that.. how and why is this happening ??

Well mainly this is do to the Camshaft having to under cut the base circle in order to make higher Lift numbers so that the clearance issues on the r53 Head are minimumized !! SO.. with the basce circle in at 1.181" this allows the correct pre-load on the hyd lifter. ( or it sets the lifter at a certain position in the rocker arm). Using the BMW Schrick camshaft as an example.. Using the stock 1.181 base circle..the max lift at the valve is .350 " Lift !! and Schrick says to 'ding the sparkplug tube for clearance' Cool??

SO.. if you have a camshaft that is showing ANYTHING over the .350 @ the Valve ( exhaust)... they have under cut the base circle to get more lift and no clearance issues !! And when the 1.181" is made smaller for more lift ( like 1.140 ) that it now unloads the Lifter by .041" !! OMG !! The lift on the cam lobe is correct !! it is at .395" open at the valve. However with the load off the lifter.. actual lift is going to be less than that !!

What to do.... Well the way to remidy the issue is to add a lash cap to the tip if the valve and remove the add'l clearance from the under cut base circle. Lash caps are in certian thicknesses !! And to add to the exhaust and then different to the intake, we decided to KISS !! Or Camshaft is designed to run with certian thikness caps, replacing to the correct pre-load. Now we can have over .450" intake lift .. and more than .388 -.400 exhaust lift ( and no interference issues) Insuring the valve spec follows the Cam lobe as intended.